Electrochemical cells are widely used for electrochemical and biological applications. Typically, as shown in FIG. 1, an electrochemical cell 10 has a working electrode 12, a non-current carrying reference electrode 14 and a counter electrode 16. Controlling and measuring the electrical parameters of an electrode reaction in a cell is done by potential, current and charge control means. The two most common modes of operation are the potential control or potentiostatic mode and the current control or galvanostatic mode. A review article by R. Greef covering this subject matter is published in Journal of Physics E, Scientific Instruments, Vol. 11, 1978, pages 1-12 (printed in Great Britain).
Modern potentiostatic control systems for use with electrochemical cells usually use an operational amplifier 18 in a feedback control configuration as shown in FIG. 1. These operational amplifiers are voltage amplifiers whose output voltage, V.sub.o, is linearly proportional to the difference between two input voltages (V.sub.in -V.sub.r). Because of the extremely high voltage gain K of operational amplifiers, V.sub.o is of such a magnitude that the voltage induced in the reference electrode V.sub.r is virtually equal to V.sub.in. Specifically, the voltage V.sub.o applied across the cell causes a cell current to flow of such magnitude that the corresponding V.sub.r is equal to V.sub.in. In other words, the voltage source (here the operational amplifier) induces a cell current which is related to V.sub.r and so acts as a source of current in the sense described in U.S. Pat. No. 3,855,101.
This type of potentiostatic control systems exhibit instabilities due to both electrochemical cell impedance, cell current monitoring circuits and the roll off characteristics of the operational amplifier. To improve the stability of these systems they are operated with a restricted bandwidth. These systems also require an additional high current device to measure the current which increases the cost and increases the problems of thermal stability. In addition, changing from a potentiostatic control mode to a galvanostatic mode is difficult and requires several other components.